These fences are called "slate armor." The idea of them is when a
conical-shaped RPG round (which is favored by insurgents most for
its multi-purpose abilities), the cone part gets jammed in the
slots of the armor, whcih stops the round from scoring a direct hit
on the hull. If it hits the slate just right, it doesn't explode on
contact, but when the rocket fuse wears down after about 4.95
seconds, it explodes, which the Stryker's regular armor can very
easily handle since it's not a direct hit on the hull. If it hits
one of the bars separating each slate hole, the slate bars will
still be able to handle the explosion by itself, but nonetheless
leaving a decent sized hole in the armor with no effect of the
Stryker cabin.
